(1) Field of the Invention
The present invention pertains to multiple custom telephone calling features and more particularly to an arrangement for controlling these custom calling features which interface with one another in a common central office.
(2) Description of the Prior Art
As computerization was introduced into telephone switching offices, it was understood that more complex functions could be provided by the switching office. Among these functions are such features as special ticketing and billing arrangements and custom calling features such as three way calling, call forwarding, speed calling, and call waiting. To implement each of these special custom calling features complex hardware in the form of trunk circuits and complex programs in the central processing unit of the switching office are required.
When these custom calling features interface with one another further complexity is added to both the trunking arrangement and the program. Among these features the more complex are call waiting and three way calling. These features are the most complex since they require the greatest amount of hardware and program to handle their operation. Call waiting service is defined as: A call waiting subscriber will hear a short tone, if he is already using his line and the second party is attempting to reach him. The second party receives normal ring back tone and the line is split, so that only the subscriber to be called will hear the short tone. The tone will be repeated in 10 seconds as a reminder, and if unanswered, the second party will receive ring back tone. If the subscriber wants to end his first call he simply hangs up and his phone will ring with the second party on the line. If he wants to hold the first party while answering the second, he presses the hookswitch for one-half a second. With this method he can switch between parties at will.
Three way calling service is defined as: A three way calling subscriber can add a third party to an existing conversation. While the subscriber is conversing with another party, a third party can be added to the conversation by depressing his hookswitch for one-half a second. This puts the original party on hold, and the subscriber will hear a special dial tone (3 spurts of tone followed by regular dial tone). He can then dial the third party and hold a private conversation with the third party. To establish the three way connection the subscriber must again depress its hookswitch for one-half a second. If the third party did not answer or if the subscriber wants to drop a third party from the three way call, he simply depresses his hookswitch for one-half a second and the original parties are re-established (and the subscriber may again establish a three way call). To disconnect, the subscriber simply hangs up and all connections will be broken down.
These custom calling features required specialized trunk arrangements and complex program for the manipulation of the connection of parties in reponse to hookswitch flashing. Arrangements for connecting custom calling subscribers individually are shown in an article entitled "Custom Calling Services on No. 1 EAX" by J. D. McLean in the GTE Automatic Electric Technical Journal, July, 1976, Vol. 15-No. 3. This article shows basic configurations for the establishment of call waiting and three way calling custom features as independent calls. This article shows the special trunks and junctors which were developed for the implementation of these custom calling features. However, the article does not deal with the interconnection of these custom calling features to one another and the resulting complexity added by this arrangement.
One manner in which to handle the problem of interacting custom calls is to prevent subscribers from calling other subscribers who have active custom calling features. This is not a suitable solution since certain subscribers would be unable to reach whomever they chose to call. Another solution is to provide complex trunks or to increase the logic of the controlling program to accommodate all the interactions of two interacting custom calls. However this situation resulted in expensive trunk arrangements which are undesirable since they increase the cost of the custom calling feature to the subscriber.
The above mentioned problems are further compounded when both of the interacting custom calls are made from the same switching office. This situation means that one switching office must control the operation of multiple custom calls making the interacting decisions very complex.
Accordingly it is the object of the present invention to provide a simple trunking arrangement and program for the operation of multiple interacting custom calls within a particular telephone switching office for a three way calling subscriber, initiating a three way call to a call waiting subscriber who is busy in an existing call.